Reaction product of a mixed ferrite and lead titanate



June 2 1953 G. BERGE REACTIQN PRODUCT OF A MIXED FERRITE AND LEADTITANATE File d June 26, 1948 9 TEM 5/1550 o/v Fe 0 ,270, M90, Mn 0 I20lbo srs MF/1350 o/v F2 ,Zn 0, Nl o 642086 JJJJD FEB A D E F e H .80

A DE FI'H A4DEFGH Patented June 2, 1953 REACTION PRODUCT OF A MIXEDFERRITE AND LEAD TITANATE Godshalk Berge, Chicago, Ill., assignor toAladdin Industries, Incorporated, Chicago, III., a corporation ofIllinois Application June 26, 1948, Serial No. 35,444

14 Claims.

This invention relates to magnetic cores which form a part of the coilsand transformers of radio-frequency circuits, It relates, moreparticularly, to the composition of and the method for making a magneticcore by which many desirable and improved characteristics are impartedto radio-frequency circuits.

It is a matter of common knowledge to those skilled in the art thatselectivity, that is, the ability to select one desired frequency anddiscriminate against others, is greatly influenced by the shape of theresonance curve or sharpness of the radio circuit. A sharp circuit givesgood selectivity and sharpness, in turn, is regulated by the Q (qualityfactor) of the circuit. At frequencies within the normal broadcast band,the Q factor of the circuit is greatly influenced by the quality andcharacteristics of the magnetic core in the coil. It is a desideratum,therefore, to provide a magnetic core which introduces a high Q factor,especially one that causes the circuit to exceed the value of 100characteristic of present radio circuits.

Selectivity is but one or the important characteristics Of aradio-frequency circuit which is subject to influence by the magneticcore. There are many others. For example, the magnetic core plays animportant role in the determination of the tuning range of the radiocircuit. The present range of most radio receivers lies between 540 and1600 kc. and, of course, it is desirable to broaden the tuning range asmuch as possible without harmfully affectin other characteristics of theradio circuit.

- Still another important consideration in radio circuits is thecharacteristic of frequency stability, that is, the ability to hold aset or tuned frequency for an extended time. Invariably it is desirableto maintain the resonant frequency as constant as possible. Oneof theprincipal factors that causes changes of frequency is the influence oftemperature. Temperature changes cause expansions or contractions of thevarious elements of the radio circuit and correspondingly cause changesin 'capacitances and inductances and the frequency will changeaccordingly. Frequency changes caused by temperature change are referredto as thermal drift. Temperature changes are unavoidable, but it isconsidered possible by proper selection of materials and by properarrangement of elements to reduce the thermal drift to a minimum. Heretoo the magnetic .core plays an important part.

- It is an object of this invention to provide a new and improvedmagnetic core composition and a method for producing the same. Thecomposition of my invention is particularly adapted for the productionof magnetic cores having greatly improved operating characteristics inradio-frequency circuits; that overcomes many of the shortcomings ofmagnetic cores now in use in such circuits; that introduces into thecircuit a Q value which is much higher than the value obtained with corecompositions now in use with the result that improved selectivity issecured; that extends the tuning range of the radio circuit; that is anoutstanding improvement in markedly decreasing the thermal drift andteaches a concept by which thermal drift may be correspondingly loweredin other magnetic core compositions; that is relatively easy andeconomically manufactured of low cost and available materials, and whichforms a core of predetermined shape having sufiicient strength anddurability to withstand the forces incident to normal handling and use.

Another object is to provide a new and improved magnet-ic core and amethod for producing the same which, amongst other things, embodies theproperties described above and which is fabricated of finely dividedmaterials temporarily bonded with a heat destructible adhesive andfinally bonded to predetermined shape to produce a microporous productin the manner corresponding to the principles of powder metal- ,lurgy,.the finely divided particles remaining substantially in their originalform to provide for desirable characteristics with respect to eddycurrent losses.

Briefly described, my invention contemplates the reaction at elevatedtemperatures of the oxides of various metals, including zinc, iron, andone or more of the oxides of the metals selected from the groupconsisting of magnesium, manganese, cobalt and nickel. For instance, myinvention may be practiced by the use of a ternary system based upon theuse of iron oxide, zinc oxide and nickel oxide or iron oxide, zinc oxideand cobalt oxide, The system may be quarter-nary based upon iron oxide,zinc oxide, magnesium-oxide and manganese oxide, or it may be a livecomponent system based upon iron oxide, zinc oxide, magnesium oxide,manganese oxide and nickel or cobalt oxide. The oxides are usuallyreacted in finely divided form. and in intimate mixture. Originally themixture has very little, if any, magnetic properties, but upon reactionat the desired thermal conditions the reaction ,product is highlymagnetic and can be used advantageously in the fabrication of mag- 3netic cores having characteristics in radio-frequency circuits whichwere heretofore unobtainable with commercial core compositions.

I have found further that by the addition of titanium oxide or titaniumand lead oxides to the above compositions, the characteristics of themagnetic core can be further improved. That is, additions of limitedamounts of titanium and lead oxides, which preferably is added incombined form as lead metatitanate (PbTlOs) hereinafter referred to astitanate, further improves the turning range and the Q value of thecircuit and reduces the thermal drift characteristics of the core byoutstanding proportions. The added ingredients give considerablestrength to the molded core product to the extent that they are betterable to withstand the forces incident to normal handling and use.

In practicing my invention, I prefer to consider the invention asinvolving two distinct concepts. The first relates entirely with theproduction of the basic magnetic materials for magnetic cores, includingreaction of the oxides of iron, zinc, and one or more of the oxides ofthe metals magnesium, manganese, nickel and cobalt, to produce a producthaving high magnetic properties. The second concept is concernedentirely with the fabrication of the magnetic core from the basicmaterials alone or in admixture with the titanium and lead oxides.Although greatest benefit is derived by the addition of the latteroxides to the basic reaction product, I have found that many of thedesirable improved characteristics may be derived also by the additionof these titanium and lead oxides to the original basic ingredientsprior to their thermal reaction.

In the original mixture, the materials may be present in the ratio of 60to '75 parts of iron oxide (calculated as F8203), to 25 parts by weightof zinc oxide (calculated as ZnO), and 10 to 25 parts of one orcombinations of the other oxides which may be either nickel oxide(NiaOs), cobalt oxide (C0203), manganese oxide (M1102), or magnesiumoxide (MgO) The oxides in finely divided or powder form are intimatelymixed and heated or fired together at a temperature in the range ofabout 2200 to 2500 F. for an extended time. Ordinarily firing iscontinued for two or more hours, and I have obtained excellent resultsby reacting the mixture of oxides for three hours at 2300 to 2400 F. Theoriginal mixture before firing has very little, if any, magneticcharacteristics, but after the described thermal treatment the productis highly magnetic. The reaction product is cooled down and then reducedinto finely divided or powder form for subsequent use asa basic materialin the fabrication of magnetic cores.

In the second phase, the finely divided magnetic material, that is, thereaction product, is mixed with a binder which serves to imparttemporary mechanical strength immediately to a formed mass of thereaction product enabling the substances to be molded to desired shapesin the usual manner. The molded composition is then heat treated atabout1900 to 2200 F. for about an hour or more. Excellent cores result fromthe heat treatments of about one and onehalf hours at 2050 F., or onehour at 2200 F., after which the heat treated core is cooled to roomconditions. I prefer to cool the heat treated product rather slowly forbest results, for example, I prefer to cool the core from a temperatureof 2050 or 2200 F. at the rate of about F. per hour. My invention,however, should not be limited to these conditions as higher or lowertemperatures may be used to advantage, and correspondingly longer orshorter times in heat treatment may be used because heat treatment,cooling, and cooling rate is greatly influenced by the mass. of materialinvolved.

When an organic binder is used originally to secure the particles inmolded form, the binding property generally is of temporary characterwhich holds the particles in the desired arrangement until the heattreatment is effective to cause bonding such as is experienced in powdermetallurgy. The organic binder will for the most part be burned off atthe temperature of heat treatment and very little effect will be hadthereof as a binder or as an insulator in the final product. Suitableorganic binders may be based on liquid or solvent solutions of variousadhesive resins such as the phcnol-aldehydes, urea ormelamine-aldehydes, vinyl polymers and copolymers, polyacrylates, rubberbased materials, polystyrene and the like. The amount of bindergenerally is influenced by the constituents of which it is formed, theparticle size and character of the base materials, and the pressuresunder which the core is molded. I prefer to use the least amount ofbinder necessary. I have successfully molded cores with as little as 2per cent binder. However, 3 per cent binder gives excellent results andnot infrequently as much as 6 or 8 per cent have been used. In anyevent, the final product is of a microporous nature, in which the mixedheat treated constituents for the most part are in their original form.

It is in this latter stage of the process that I prefer to add theoxides of titanium or the oxides or titanium and lead. I have securedbest results when these latter oxides are added in combined form, suchas titanate. The use of titanate as a constituent with my basicmaterials, comprises a cardinal feature of my invention. By the use oftitanate cores are produced which favorably influence the radio circuitwith respect to Q values and tuning range. By the additions of titanate,the thermal drift of the core is reduced by outstanding proportions. Theadditions of the oxides of titanium and lead appear greatly to improvethe strength of the molded product subjected to a heat treatment. To thebest of our knowledge, the additives become binding agents for thematrix of base materials because the coherence and the strength of thecore increases according to the amount of titanate used.

By Way of illustration but not by way of limitation, the followingexamples illustrate the manner for practicing my invention.

Example 1 (composition B in the graphs) A mixture constituted of 69parts iron oxide (FezOs) 17 parts zinc oxide (ZnO) 10 parts manganeseoxide (MnOz) and four parts magnesium oxide (MgO) in finely divided orpowder form, is fired at about 2300 to 2400 F. for about three hours.The original mixture is relatively nonmagnetic. The cooled reactionproduct, however, has highly magnetic characteristics. The cooled massis friable and is reduced to finely divided form to comprise a'basematerial which may be used as is for magnetic core formation.

To the granular reaction product described, there is admixed sufiiicientliquid binder, such as 2-3 per cent by weight of a phenolic resinadvanced to an intermediate stage of polymeric growth, a soluble stage,and the mass is thenformedinthe usual manner, such as by molding one totwo hours and then cooleddown slowly in steps of 100 degrees per houruntil a temperature of 500 or 600 F. is reached. The resultant productis a molded core having the improved characteristics shown by the letterB in the accompanying graphs. It will be noted that the tuning band isextended to include 390 and 1650 kc. as compared to the limitation to540 and 1600 kc. of prior materials. A very marked and beneficialimprovement is had in the Q value, which with core composition formed inmy first example is in the range of 170 as compared to 100 of the priorart. To a lesser extent the thermal drift is helpfully lowered.

Erample12 (composition C in the graphs) To 98 parts of the reactionproduct of Example 1, 2 parts by weight of titanate (PbTiOs) was addedprior to or in conjunction with the admixture of the liquid binder. Therequired amount of material is molded under 1000 to 2000 pounds persquare inch pressure to core shape which is then heat treated at about2000 F. for one and one-half hours. Upon slowly cooling the heat treatedcore, it was found that the strength characteristic of the moldedproduct was unexpectedly improved. More important, however, was thenotable improvement in thermal drift. By the addition of 2 per centtitanate at this stage of the process, the thermal drift was loweredfrom an acceptable value of 0.020 to an astonishingly low value of 0001.Instead of carrying out the heat treatment at 2000' F. it may be carriedout for one hour at 2200 F. Further improvement is also secured in the Qvalue which rises to 1'74.

Example 3 (composition D in the graphs) I form a basic 3 phase system bycombining in intimate mixture of 66 parts by weight iron oxide (FezOs)17 parts by weight zinc oxide (ZnO) and 17 parts by weight nickel oxide(Ni2O3). The ingredients may be fired for two hours at about 2500 F.during which a reaction takes place that converts these materials incombination from their original non magnetic properties to a high- 1ymagnetic substance. The cooled and friable mass comprising the reactionproduct is reduced in finely divided form to comprise a materialsuitable for molding magnetic cores.

Magnetic core formation is efiected by the addition thereto of about 2-3per cent solution of the reaction product of the urea-formaldehyde insuitable solvent and the subsequent molding under 500-A000 pounds persquare inch to desired core shape. The molded composition is heattreated for one hour at 2200 F. and then slowly cooled at about 100degrees per hour to room temperature. The nickel oxide in the aboveformulation may be partially or wholly replaced by cobalt oxide or theoxides of manganese and magnesium. Instead of 3 per centurea-formaldehyde solution, other binders in greater or lesserproportion may be used.

Example 4 (composition E in the graphs) To the base composition orfinely divided reaction product of Example 3, there is added about 2 percent titanate and the core formation is effec'ted in the mannerdescribed above by the ad'- di'ti'on of a temporary resinous binder andmolding in the usual manner. The molding may beheat treated for abouttwo hours at 1900 F. and slowly cooled to produce a very desirable mag"-netic core. By "refer nce to the graphs it W111 be evident that theaddition of titanate was instrumental in extending the tuning range,increasing the Q value of the circuit to above'200, andnoticeablyreducing the thermal drift from that originally secured by thebase ingredients.

Example 5 (composition F in the graphs) To 96 parts of the reactionproduct of Example 3, there .is added '4 parts by weight of titanate,and from this composition a core is formed in the usual manner of binderincorporation followed by the heat treatment at about 2100 F. fortwohours. The increased amount of titanate causes very little change inthe tuning band range or the Q value of the circuit which exceed presentstandards by a wide margin. The increased amount of titanate lowers byoutstanding proportions the thermal drift of the resulting magneticcoreand its presence is felt in the resulting increased strength of thecore.

Example 6 (composition G in the graphs) To 94 parts of the reactionproduct of Example 3, there is added 6 parts by weight of titanate. Thecomposition is carried through the steps of binder incorporation,molding, heat treatment and cooling in the manner described inconnection with Examples l and 5. Although the Q value of the circuit islowered by the presence of the increased amount of titanate, it is stillabove the present value of 100. Important is the drastic reduction inthermal drift as shown in the graphical illustrations.

Example 7 (composition H in the graphs) To 92 parts of the reactionproduct Of Example 3, there is added 8 parts by weight of titanate. Thecomposition is admixed with suitable organic binder and heat treated,then molded to form, at about 2200 F. for one and one-half hours. Thegreater proportion of titanate markedly improves the physical strengthof the heat treated core. This may be caused by the greater amount ofwhat may be a more fusible material which functions as a binding agentor it may be the result of better densification resulting in the moldingstep. The resulting product introduces a Q value of into the circuitwhich is still above present standards. The frequency range isextended-to 390 to 1650 kc. and the thermal drift is further reduced byan appreciable amount. From these results there is reason to believethat considerable benefit-would be derived from the use of increasedamounts of titanate, that is about 10 or 12 per cent. Obviously, thethermal drift, which is a very important characteristic in radio andhigh frequency circuits, is favorably influenced by its presence. v V

In making these tests on the core, a standard coil was used having aprogressive universal winding of 492 turns 7-44. S. S. E. wire in oneand three-eighths inch space on a tubing having 0.221 outside diameter.I

Referring now to the graphs, a composition theoretically possessing theacceptable characteristics of magnetic cores in present use isdesignated by the letter A. Letters B, C, D, E, F, G and H correspond tothe compositions of Examples 1 to 7 respectively. By comparing thegraphical illustrations, the significance ermine axioms importance of myinvention will become immedately apparent.

For example, compared to standard values, the composition B of Example 1extends the tuning range by 200 kc., there is a marked improvement inthe Q values of the circuit, and the thermal drift is benefitted. Theaddition of titanate (C) is outstanding for its unprecedented andunexpected improvement which it imparts to the thermal driftcharacteristics.

Turning now to the compositions based on the system zinc oxide, ironoxide and nickel oxide, marked improvement is shown in the influence onthe Q factor of the circuit by the care of composition D (Example 3). Bythe additions of titanate in increasing amounts noticeable reduction inthermal drift is secured and the tuning range is steadily extended. Vastimprovements in the Q value of the circuit is shown when up to 6 percent titanate is used and the values are still above normal when 8 percent is used.

The thermal drift continues to decrease with the addition of more than 6per cent titanate and by extrapolation should almost approach zero valueat about 10 or 12 per cent. Where low thermal drift is important, lowerQ values can be tolerated and therefore it is expected that even greaterproportions of lead and titanium oxides might be used.

It will be apparent from the foregoing description that I have produceda new and improved core composition and materials for producing thesame, having many properties and characteristics which exceed normalexpectations Without harmfully affecting other characteristics desiredin a suitable magnetic core. My invention also illustrates a new conceptfor manufacturing magnetic cores for radio circuits out of finelydividing the metal oxides which are thermally reacted to produce acomplex compound which for the present is unknown, the compoundpossesses the improved characteristics described. It illustrates aprocess by which magnetic cores may be economically formed of selectedmetal oxides converted by heat treatment to magnetic characteristics andthe production of a microporous body having adequate physical strengthto resist the forces incident to normal handling and use and in whicheddy currents are held to a minimum. It sets forth the novel use oftitanium oxides or titanium and lead oxides in proportions of about 12per cent or less .by weight to impart noticeable improvements in Q valueof the circuit tuning range and outstanding reduction in thermal drift.It will be understood that the values in thermal drift secured bycomposition D and E may be compensated to the extent that the coreintroducing excellent Q value to the circuit may be used to advantage inradio circuits.

While the ultimate object of this invention is the production of amagnetic core, it will be readily understood that the fired basecomposition is likewise an article of commerce and comprises subjectmatter of this invention. It will be also understood that the titaniumoxide or combined titanium and lead oxides may be originallyincorporated with the base ingredients to be fired, and that numerousother changes in amounts and types of materials as well as conditions oftreatment may be made without departing from the spirit of the inventionespecially as defined in the following claims.

I claim:

1. A magnetic core formed of the thermal reaction product of leadmetatitanate with the thermal reaction product of iron oxide calculatedas Fezos, zinc oxide calculated as ZnO and the oxide of a metal selectedfrom the group con-sisting of magnesium, manganese, nickel and cobaltand mixtures thereof calculated as MgO, MnO, Ni2O3 and C0203respectively.

2. A magnetic core formed of the reaction product of up to 12 percent byweight lead metatitanate with the thermal reaction product of iron oxidecalculated as F6203, zinc oxide calculated as ZnO and the oxide of ametal selected from the group consisting of magnesium, manganese, nickeland cobalt and mixtures thereof calculated as MgO, MnO NizOs, and C0203respectively.

3. A magnetic core formed of the thermal reaction product of a mixtureof metal oxides in particle form present in the ratio of 60-75 percentby weight iron oxide calculated as FezOs, 10-25 percent by weight zincoxide calculated as ZnO, and 10-25 percent by weight of the oxide of ametal selected from the group consisting of magnesium, manganese, nickeland cobalt and mixtures thereof calculated as MgO, MnO, NizOa and C0203respectively, and up to 12 percent by weight of the oxides of lead andtitanium calculated as PbTiOz.

4. A magnetic core formed of the product of reaction at a temperaturewithin the range of 1900-2200 F. between lead metatitanate in amounts upto 12 percent by weight with the product of reaction at a temperaturerange within 2200-2500 F. of iron oxide calculated as F8203, zinc oxidecalculated as ZnO and the oxide of a metal selected from the groupconsisting of magnesium, manganese, cobalt, nickel and mixtures thereofcalculated as MgO, MnO, C0203 and Ni2O3 respectively.

5. A magnetic core material formed of the product of reaction at atemperature within the range of l900-2200 F. between the oxides of leadand titanium calculated as lead metatitanate with the product of thereaction at a temperature Within the range of 2200-2500 F. between metaloxides present in the ratio of 60-75 percent by weight iron oxidecalculated as FezOs, 10-25 percent by weight zinc oxide calculated asZnO, and 10-25 percent by weight of the oxides selected from the metalsconsisting of magnesium, manganese, nickel, cobalt and mixtures thereofcal culated as MgO, MnO, M203 and C0203 respectively.

6'. In the method of preparing materials for magnetic cores, the stepsof firing a mixture of iron oxide calculated as F6203, zinc oxidecalculated as ZnO, and the oxides of a metal selected from the groupconsisting of magnesium, manganese, cobalt, nickel and mixtures thereofcalculated as MgO, MnO, C0263 and NizOa respectively at a temperaturewithin the range of 2000-2500 F. for more than 2 hours and thermallyreacting the reaction product in finely divided form with leadmetatitanate at a temperature within the range of l900-2200 F. for morethan 1 hour.

'7. In the method of preparing materials for magnetic cores, the stepsof firing a mixture of iron oxide calculated as F8203, zinc oxidecalculated as ZnO, and the oxides of a metal selected from the groupconsisting of magnesium, manganese, cobalt, nickel and mixtures thereofcalculated as MgO, MnO, 00203 and NizOs respectively at a temperaturewithin the range of 2000-2500 F. for more than 2 hours and thermallyreacting the reaction product in finely divided form with leadmetatitanate in amounts ranging up to 12 percent by weight of thecomposition at a temperature within the range of 1900-2200 F. for morethan one hour and then cooling the reaction mixture gradually to atemperature of 600 F. and then to room temperature.

8. In the method of preparing a magnetic core, the steps of reacting amixture of finely divided metallic oxides present in the ratio of 60-75percent by weight iron oxide calculated as FezOa, -25 percent by weightzinc oxide calculated as ZnO, and 10-25 percent by weight of the oxidesof a metal selected from the group consisting of manganese, magnesium,nickel and cobalt calculated as MnO, MgO, NizOs and C0203 respectivelyat temperatures in the range of 2200*- 2500 F. for more than 2 hours,subdividing the reaction product, reacting the subdivided reactionproduct With up to 8 percent by weight of lead and titanium oxidescalculated as PbTiOa in combination with sufficient resinous bindertemporarily to hold the particles in predetermined shape until theparticles become thoroughly bonded at reaction temperature of 1900-2200F., and then cooling the molded core gradually to room conditions.

9. In the method of preparing a magnetic core, the steps of reacting amixture of finely divided metallic oxides present in the ratio of 60-75percent by weight iron oxide calculated as FezOs, 10-25 percent byweight zinc oxide calculated as ZnO, and 10-25 percent by weight ofnickel oxide calculated as NizOs at temperatures in the range of2200-2500 F. for more than 2 hours, subdividing the reaction product,reacting the subdivided reaction product with up to 8 percent by weightof lead and titanium oxides calculated as PbTiO3 in combination withsufficient resinous binder temporarily to hold the particles inpredetermined shape until the particles become thoroughly bonded atreaction temperature of 1900 2200 F., and then cooling the molded coregradually to room conditions.

10. In the method of preparing a magnetic core, the steps of reacting amixture of finely divided metallic oxides present in the ratio of 60-75percent by weight iron oxide calculated as F6203, 10-25 percent byweight zinc oxide calculated as ZnO, and 10-25 percent by weight cobaltoxide calculated as C0203 at temperatures in the range of 2200-2500 F.for more than 2 hours, subdividing the reaction product, reacting thesubdivided reaction product with up to 8 percent by weight of lead andtitanium oxides calculated as PbTiOa in combination with sufficientresinous binder temporarily to hold the particles in predetermined shapeuntil the particles become thoroughly bonded at reaction temperature of1900- 2100 F., and then cooling the molded core graduually to roomconditions.

11. In the method of preparing a magnetic core,

the steps of reacting a mixture of finely divided metallic oxidespresent in the ratio of 60-75 percent by weight iron oxide calculated asF6203, 10-25 percent by Weight zinc oxide calculated as ZnO, and 10-25percent of a mixture of manganese oxide calculated as D/InO andmagnesium oxide calculated as MgO at temperatures in the range of2200-2500 F. for more than 2 hours, subdividing the reaction product,reacting the subdivided reaction product with up to 8 percent by weightof lead and titanium oxides calculated as PbTiOs in combination withsufficient resinous binder temporarily to hold the particles inpredetermined shape until the particles become thoroughly bonded atreaction temperature of 1900-2200 F., and then cooling the molded coregradually to room conditions.

12. In the method of manufacturing a bonded magnetic core, the steps ofthermally reacting a mixture of finely divided metallic oxides presentin the ratio of 60-75 percent by weight iron oxide calculated as F6203,10-25 percent by Weight zinc oxide, calculated as ZnO, 10-25 percent byweight of the oxide of a metal selected from the group consisting ofmagnesium, manganese, cobalt and nickel and mixtures thereof calculatedas MgO, MnO, C0203 and NizOs respectively, for at least two hours at atemperature in the range of 2200-2500 F., subdividing the reactionproduct to particle form, thermally reacting a mixture of the subdividedreaction product with up to 8 percent by weight lead metatitanate afterforming the particles to predetermined shape with less than 8 percent byweight organic resinous binder which functions as a temporary binderuntil an interbonded relation is established by thermal reaction forover one hour at a temperature within the range of 1900-2200 F., andthen cooling the product at the rate of about F. per hour until atemperature of 600 F. is reached, and then cooling to room temperature.

13. A magnetic core prepared by the method of claim 7.

14. A magnetic core prepared by the method of claim 12.

GODSHALK BERGE'.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,292,206 Woodrufi Jan. 21, 1919 1,946,964 Cobb Feb. 13, 19341,976,230 Kato Oct. 6, 1934 2,443,636 Nesbit June 22, 1948 2,452,529Snoek Oct. 26, 1948 2,452,530 Snoek Oct. 26, 1948 2,452,531 Snoek Oct.26, 1948 2,462,162 Christensen et al. Feb. 22, 1949 2,496,346 Haayman etal Feb. 7, 1950

1. A MAGNETIC CORE FORMED OF THE THERMAL REACTION PRODUCT OF LEADMETATITANATE WITH THE THERMAL REACTION PRODUCT OF IRON OXIDE CALCULATEDAS FE2O3, ZINC OXIDE CALCULATED AS ZNO AND THE OXIDE OF A METAL SELECTEDFROM THE GROUP CONSISTING OF MAGNESIUM, MANGANESE, NICKEL AND COBALT ANDMIXTURES THEREOF CALCULATED AS MGO, MNO, NI2O3 AND CO2O3 RESPECTIVELY.